It is well known in the industry that in order to process polyvinyl chloride into useful articles, a heat stabilizer must be incorporated into the compound to prevent polymer degradation. Typically, these stabilizers are bivalent metal ion salts of fatty acids or alkyl phenols alone or in combination with organic phosphite esters. The metal ions used are barium, calcium, cadmium, strontium, zinc, lead and tin. Effective heat stabilizers for polyvinyl chloride are tin compounds and combinations of barium and zinc or barium, cadmium and zinc alone or with the addition of an organic alkyl aryl phosphite. While these stabilizers are effective, their use is often limited due to their high cost or toxicological properties. In many case, non-toxic combinations of calcium and zinc must be used, even though they are much less effective.
The use of dicyandiamide (cyanoguanidine) has been recognized as a heat stabilizer for vinyl chloride copolymers. Several patents have been granted for the use of dicyandiamide, melamine, guanidine and chemically similar compounds as heat stabilizers specifically for vinyl chloride-vinyl acetate copolymers filled with asbestos for flooring compounds. No reference has been found, however, to its use singly or in combination with, for example, an organic salt of calcium, in stabilizing vinyl chloride dispersion resins. Dispersion resins, because of their use in plasticizer paste form, generally make use of liquid heat stabilizers in organic solvent mediums.